Publications from researchers at the Buck Institute for Research on Aging http://www.buckinstitute.org/jasperLab © 2011 Buck Institute, All Rights Reserved Epithelial homeostasis in the posterior midgut of Drosophila is maintained by multipotent intestinal stem cells (ISCs). ISCs selfrenew and produce enteroblasts (EBs) that differentiate into either enterocytes (ECs) or enteroendocrine cells (EEs) in response to differential Notch (N) activation. Various environmental and growth signals dynamically regulate ISC activity, but their integration with differentiation cues in the ISC lineage remains unclear. Here we identify Notchmediated repression of Tuberous Sclerosis Complex 2 (TSC2) in EBs as a required step in the commitment of EBs into the EC fate. The TSC1/2 complex inhibits TOR signaling, acting as a tumor suppressor in vertebrates and regulating cell growth. We find that TSC2 is expressed highly in ISCs, where it maintains stem cell identity, and that Nmediated repression of TSC2 in EBs is required and sufficient to promote EC differentiation. Regulation of TSC/TOR activity by N signaling thus emerges as critical for maintenance and differentiation in somatic stem cell lineages. http://www.ncbi.nlm.nih.gov/pubmed/23144631 Sat, 31 Dec 2011 00:00:00 -0800 Studies on stem cell aging are uncovering molecular mechanisms of regenerative decline, providing new insight into potential rejuvenating therapies. http://www.ncbi.nlm.nih.gov/pubmed/22926561 Sat, 31 Dec 2011 00:00:00 -0800 Tissue recovery after injury requires coordinated regulation of cell repair and apoptosis, removal of dead cells, and regeneration. A critical step in this process is the recruitment of blood cells that mediate local inflammatory and immune responses, promoting tissue recovery. Here we identify a new role for the transcriptional regulator Schnurri (Shn) in the recovery of UVdamaged Drosophila retina. Using an experimental paradigm that allows precise quantification of tissue recovery after a defined dose of UV, we find that Shn activity in the retina is required to limit tissue damage. This function of Shn relies on its transcriptional induction of the PDGFlike growth factor pvf1, which signals to tissueassociated hemocytes. We show the pvf1 receptor, PVR, acts in hemocytes to induce a macrophagelike morphology, and that this is required to limit tissue loss after irradiation. Our results identify a new Shnregulated paracrine signaling interaction between damaged retinal cells and hemocytes ensures recovery and homeostasis of the challenged tissue. http://www.ncbi.nlm.nih.gov/pubmed/22275438 Sat, 31 Dec 2011 00:00:00 -0800 Longterm maintenance of tissue homeostasis relies on the accurate regulation of somatic stem cell activity. Somatic stem cells have to respond to tissue damage and proliferate according to tissue requirements while avoiding overproliferation. The regulatory mechanisms involved in these responses are now being unraveled in the intestinal epithelium of Drosophila, providing new insight into strategies and mechanisms of stem cell regulation in barrier epithelia. Here, we review these studies and highlight recent findings in vertebrate epithelia that indicate significant conservation of regenerative strategies between vertebrate and fly epithelia. http://www.ncbi.nlm.nih.gov/pubmed/22056138 Fri, 31 Dec 2010 00:00:00 -0800 Metazoans adapt to changing environmental conditions and to harmful challenges by attenuating growth and metabolic activities systemically. Recent studies in mice and flies indicate that endocrine signaling interactions between insulin/IGF signaling (IIS) and innate immune signaling pathways are critical for this adaptation, yet the temporal and spatial hierarchy of these signaling events remains elusive. Here, we identify and characterize a program of signaling interactions that regulates the systemic response of the Drosophila larva to localized DNA damage. We provide evidence that epidermal DNA damage induces an innate immune response that is kept in check by systemic repression of IIS activity. IIS repression induces NFB/Relish signaling in the fat body, which is required for recovery of IIS activity in a second phase of the systemic response to DNA damage. This systemic response to localized DNA damage thus coordinates growth and metabolic activities across tissues, ensuring growth homeostasis and survival of the animal. http://www.ncbi.nlm.nih.gov/pubmed/21664581 Fri, 31 Dec 2010 00:00:00 -0800 Regulated adhesion between cells and their environment is critical for normal cell migration. We have identified mutations in a gene encoding the Drosophila hydrogen peroxide (HO)degrading enzyme Jafrac1, which lead to germ cell adhesion defects. During gastrulation, primordial germ cells (PGCs) associate tightly with the invaginating midgut primordium as it enters the embryo however, in embryos from jafrac1 mutant mothers this association is disrupted, leaving some PGCs trailing on the outside of the embryo. We observed similar phenotypes in embryos from DEcadherin/shotgun (shg) mutant mothers and were able to rescue the jafrac1 phenotype by increasing DEcadherin levels. This and our biochemical evidence strongly suggest that Jafrac1mediated reduction of HO is required to maintain DEcadherin protein levels in the early embryo. Our results present in vivo evidence of a peroxiredoxin regulating DEcadherinmediated adhesion. http://www.ncbi.nlm.nih.gov/pubmed/21316590 Fri, 31 Dec 2010 00:00:00 -0800 Precise control of somatic stem cell proliferation is crucial to ensure maintenance of tissue homeostasis in highturnover tissues. In Drosophila, intestinal stem cells (ISCs) are essential for homeostatic turnover of the intestinal epithelium and ensure epithelial regeneration after tissue damage. To accommodate these functions, ISC proliferation is regulated dynamically by various growth factors and stress signaling pathways. How these signals are integrated is poorly understood. Here, we show that EGF receptor signaling is required to maintain the proliferative capacity of ISCs. The EGF ligand Vein is expressed in the muscle surrounding the intestinal epithelium, providing a permissive signal for ISC proliferation. We find that the AP1 transcription factor FOS serves as a convergence point for this signal and for the Jun Nterminal kinase (JNK) pathway, which promotes ISC proliferation in response to stress. Our results support the notion that the visceral muscle serves as a functional 'niche' for ISCs, and identify FOS as a central integrator of a nichederived permissive signal with stressinduced instructive signals, adjusting ISC proliferation to environmental conditions. http://www.ncbi.nlm.nih.gov/pubmed/21307097 Fri, 31 Dec 2010 00:00:00 -0800 In Drosophila, intestinal stem cells (ISCs) respond to oxidative challenges and inflammation by increasing proliferation rates. This phenotype is part of a regenerative response, but can lead to hyperproliferation and epithelial degeneration in the aging animal. Here we show that Nrf2, a master regulator of the cellular redox state, specifically controls the proliferative activity of ISCs, promoting intestinal homeostasis. We find that Nrf2 is constitutively active in ISCs and that repression of Nrf2 by its negative regulator Keap1 is required for ISC proliferation. We further show that Nrf2 and Keap1 exert this function in ISCs by regulating the intracellular redox balance. Accordingly, loss of Nrf2 in ISCs causes accumulation of reactive oxygen species and accelerates agerelated degeneration of the intestinal epithelium. Our findings establish Keap1 and Nrf2 as a critical redox management system that regulates stem cell function in highturnover tissues. http://www.ncbi.nlm.nih.gov/pubmed/21295275 Fri, 31 Dec 2010 00:00:00 -0800 Cellular responses to extrinsic and intrinsic insults have to be carefully regulated to properly coordinate cytoprotection, repair processes, cell proliferation and apoptosis. Stress signaling pathways, most prominently the JunNterminal Kinase (JNK) pathway, are critical regulators of such cellular responses and have accordingly been implicated in the regulation of lifespan in various organisms. JNK signaling promotes cytoprotective gene expression, but also interacts with the insulin signaling pathway to influence growth, metabolism, stress tolerance and regeneration. Here, we review recent studies in Drosophila that elucidate the tissuespecific and systemic consequences of JNK activation that ultimately impact lifespan of the organism. http://www.ncbi.nlm.nih.gov/pubmed/21111799 Fri, 31 Dec 2010 00:00:00 -0800 Hormonal regulation of glucose and lipid metabolism is pivotal for metabolic homeostasis and energy balance. Two studies in this issue of Cell (Mihaylova etal., 2011 and Wang etal., 2011) introduce a new conserved signaling mechanism controlling catabolic gene expression: class IIa histone deacetylases (HDACs) regulate Foxo activity in Drosophila and mice. http://www.ncbi.nlm.nih.gov/pubmed/21565608 Fri, 31 Dec 2010 00:00:00 -0800 Caloric intake influences metabolic homeostasis, somatic maintenance, tissue regeneration, and longevity inmetazoans. Recent studies indicate that nutrientdependent changes in stem cell populations play an important role in these effects. Here, we review the emerging picture of how nutrientsensing pathways affect stem cell behavior, providing a mechanism to influence life span. http://www.ncbi.nlm.nih.gov/pubmed/21109189 Thu, 31 Dec 2009 00:00:00 -0800 Regenerative processes are critical to maintain tissue homeostasis in highturnover tissues. At the same time, proliferation of stem and progenitor cells has to be carefully controlled to prevent hyperproliferative diseases. Mechanisms that ensure this balance, thus promoting proliferative homeostasis, are expected to be critical for longevity in metazoans. The intestinal epithelium of Drosophila provides an accessible model in which to test this prediction. In aging flies, the intestinal epithelium degenerates due to overproliferation of intestinal stem cells (ISCs) and misdifferentiation of ISC daughter cells, resulting in intestinal dysplasia. Here we show that conditions that impair tissue renewal lead to lifespan shortening, whereas genetic manipulations that improve proliferative homeostasis extend lifespan. These include reduced Insulin/IGF or JunNterminal Kinase (JNK) signaling activities, as well as overexpression of stressprotective genes in somatic stem cell lineages. Interestingly, proliferative activity in aging intestinal epithelia correlates with longevity over a range of genotypes, with maximal lifespan when intestinal proliferation is reduced but not completely inhibited. Our results highlight the importance of the balance between regenerative processes and strategies to prevent hyperproliferative disorders and demonstrate that promoting proliferative homeostasis in aging metazoans is a viable strategy to extend lifespan. http://www.ncbi.nlm.nih.gov/pubmed/20976250 Thu, 31 Dec 2009 00:00:00 -0800 http://www.ncbi.nlm.nih.gov/pubmed/20157572 Wed, 31 Dec 2008 00:00:00 -0800 Adaptation to environmental challenges is critical for the survival of an organism. Repression of Insulin/IGF Signaling (IIS) by stressresponsive JunNterminal Kinase (JNK) signaling is emerging as a conserved mechanism that allows reallocating resources from anabolic to repair processes under stress conditions. JNK activation in Insulinproducing cells (IPCs) is sufficient to repress Insulin and Insulinlike peptide (ILP) expression in rats and flies, but the significance of this interaction for adaptive responses to stress is unclear. In this study, it is shown that JNK activity in IPCs of flies is required for oxidative stressinduced repression of the Drosophila ILP2. It is found that this repression is required for growth adaptation to heat stress as well as adult oxidative stress tolerance, and that induction of stress response genes in the periphery is in part dependent on IPCspecific JNK activity. Endocrine control of IIS by JNK in IPCs is thus critical for systemic adaptation to stress. http://www.ncbi.nlm.nih.gov/pubmed/19627268 Wed, 31 Dec 2008 00:00:00 -0800 Metabolic homeostasis in metazoans is regulated by endocrine control of insulin/IGF signaling (IIS) activity. Stress and inflammatory signaling pathwayssuch as JunNterminal Kinase (JNK) signalingrepress IIS, curtailing anabolic processes to promote stress tolerance and extend lifespan. While this interaction constitutes an adaptive response that allows managing energy resources under stress conditions, excessive JNK activity in adipose tissue of vertebrates has been found to cause insulin resistance, promoting type II diabetes. Thus, the interaction between JNK and IIS has to be tightly regulated to ensure proper metabolic adaptation to environmental challenges. Here, we identify a new regulatory mechanism by which JNK influences metabolism systemically. We show that JNK signaling is required for metabolic homeostasis in flies and that this function is mediated by the Drosophila Lipocalin family member Neural Lazarillo (NLaz), a homologue of vertebrate Apolipoprotein D (ApoD) and Retinol Binding Protein 4 (RBP4). Lipocalins are emerging as central regulators of peripheral insulin sensitivity and have been implicated in metabolic diseases. NLaz is transcriptionally regulated by JNK signaling and is required for JNKmediated stress and starvation tolerance. Loss of NLaz function reduces stress resistance and lifespan, while its overexpression represses growth, promotes stress tolerance and extends lifespanphenotypes that are consistent with reduced IIS activity. Accordingly, we find that NLaz represses IIS activity in larvae and adult flies. Our results show that JNKNLaz signaling antagonizes IIS and is critical for metabolic adaptation of the organism to environmental challenges. The JNK pathway and Lipocalins are structurally and functionally conserved, suggesting that similar interactions represent an evolutionarily conserved system for the control of metabolic homeostasis. http://www.ncbi.nlm.nih.gov/pubmed/19390610 Wed, 31 Dec 2008 00:00:00 -0800 Metabolic adaptation to environmental changes is crucial for the longterm survival of an organism. Signaling mechanisms that govern this adaptation thus influence lifespan. One such mechanism is the insulin/insulinlike growth factor signaling (IIS) pathway, a central regulator of metabolism in metazoans. Recent studies have identified the stressresponsive JunNterminal kinase (JNK) pathway as a regulator of IIS signaling, providing a link between environmental challenges and metabolic regulation. JNK inhibits IIS activity and, thus, promotes lifespan extension and stress tolerance. Interestingly, this interaction is also at the center of agerelated metabolic diseases. Here, we review recent advances illuminating the mechanisms of the JNKIIS interaction and its implications for metabolic diseases and lifespan in metazoans. http://www.ncbi.nlm.nih.gov/pubmed/19251431 Wed, 31 Dec 2008 00:00:00 -0800 Metazoans employ cytoprotective and regenerative strategies to maintain tissue homeostasis. Understanding the coordination of these strategies is critical to developing accurate models for aging and associated diseases. Here we show that cytoprotective Jun Nterminal kinase (JNK) signaling influences regeneration in the Drosophila gut by directing proliferation of intestinal stem cells (ISCs). Interestingly, this function of JNK contributes to the loss of tissue homeostasis in old and stressed intestines by promoting the accumulation of misdifferentiated ISC daughter cells. Ectopic Delta/Notch signaling in these cells causes their abnormal differentiation but also limits JNKinduced proliferation. Protective JNK signaling and control of cell proliferation and differentiation by Delta/Notch signaling thus have to be carefully balanced to ensure tissue homeostasis. Our findings suggest that this balance is lost in old animals, increasing the potential for neoplastic transformation. http://www.ncbi.nlm.nih.gov/pubmed/18940735 Mon, 31 Dec 2007 00:00:00 -0800 Antagonism between growthpromoting and stressresponsive signaling influences tissue homeostasis and longevity in metazoans. The transcription factor FoxO is central to this regulation, affecting cell proliferation, stress responses, apoptosis, and longevity. Insulin/IGF signaling promotes FoxO phosphorylation, causing its interaction with 1433 molecules. The consequences of this interaction for FoxOinduced biological processes and for the regulation of lifespan in higher organisms remain unclear. Significant complexities in the effects of 1433 proteins on lifespan have been uncovered in Caenorhabditis elegans, suggesting both positive and negative roles for 1433 proteins in the control of aging. Using genetic and biochemical studies, we show here that 1433epsilon antagonizes FoxO function in Drosophila. We find that dFoxO and 1433epsilon proteins interact in vivo and that this interaction is lost in response to oxidative stress. Loss of 1433epsilon results in increased stressinduced apoptosis, growth repression and extended lifespan of flies, phenotypes associated with elevated FoxO function. Our results further show that increased expression of 1433epsilon reverts FoxOinduced growth defects. 1433epsilon thus serves as a central modulator of FoxO activity in the regulation of growth, cell death and longevity in vivo. http://www.ncbi.nlm.nih.gov/pubmed/18665908 Mon, 31 Dec 2007 00:00:00 -0800 Interactions between insulin signaling and stressresponse pathways can markedly impact life span. In this issue, Tullet et al. (2008) demonstrate that the worm homolog of Nrf2, called SKN1, a transcription factor that switches on expression of antioxidant genes, is an important component of such signaling interactions. http://www.ncbi.nlm.nih.gov/pubmed/18358801 Mon, 31 Dec 2007 00:00:00 -0800 Cells damaged by environmental insults have to be repaired or eliminated to ensure tissue homeostasis in metazoans. Recent studies suggest that the balance between cell survival signals and proapoptotic stimuli controls the decision between cell repair and death. How these competing signals are integrated and interpreted to achieve accurate control over cell fate in vivo is incompletely understood. Here, we show that the Forkhead Box O transcription factor Foxo and the AP1 transcription factor DFos are required downstream of JunNterminal kinase signaling for the apoptotic response to UVinduced DNA damage in the developing Drosophila retina. Both transcription factors regulate the proapoptotic gene hid. Our results indicate that UVinduced apoptosis is repressed by receptor tyrosine kinasemediated inactivation of Foxo. These data suggest that integrating stress and survival signals through Foxo drives the decision between cell death and repair of damaged cells in vivo. http://www.ncbi.nlm.nih.gov/pubmed/17183370 Sun, 31 Dec 2006 00:00:00 -0800 Epithelial movements are key morphogenetic events in animal development. They are driven by multiple mechanisms, including signaldependent changes in cytoskeletal organization and in cell adhesion. Such processes must be controlled precisely and coordinated to accurately sculpt the threedimensional form of the developing organism. By observing the Drosophila epidermis during embryonic development using confocal timelapse microscopy, we have investigated how signaling through the JunNterminal kinase (JNK) pathway governs the tissue sheet movements that result in dorsal closure (DC). We find that JNK controls the polymerization of actin into a cable at the epidermal leading edge as previously suggested, as well as the joining (zipping) of the contralateral epithelial cell sheets. Here, we show that zipping is mediated by regulation of the integrins myospheroid and scab. Our data demonstrate that JNK signaling regulates a set of target genes that cooperate to facilitate epithelial movement and closure. http://www.ncbi.nlm.nih.gov/pubmed/16317725 Sat, 31 Dec 2005 00:00:00 -0800 Acquiring the ability to migrate is essential for cells taking part in many developmental and disease processes. Two studies in this issue of Developmental Cell use gene expression profiling of purified border cells from the Drosophila ovary to characterize the molecular changes required in cells to initiate migration in vivo. Their results offer interesting new insights into a moving cell's physiology. http://www.ncbi.nlm.nih.gov/pubmed/16580988 Sat, 31 Dec 2005 00:00:00 -0800 The role of cJun Nterminal kinase (JNK) signaling in cancer is enigmatic, and both tumorpromoting and tumorsuppressing functions have been ascribed to JNK pathway components. We have used the Drosophila eye to investigate the function of the JNK pathway in three different tumor models of increasing malignancy. Benign lesions caused by loss of the neoplastic tumor suppressor gene scribble can efficiently be eliminated by JNKinduced apoptosis. In such a scenario, the eye reverts to a wildtype phenotype, indicating that the JNK pathway prevents tumor formation. The situation changes in the case of aggressive tissue overgrowth, which can be induced by oncogenic activation of the Ras/Raf pathway in the eye, or in malignant invasive tumors resulting when Raf activation is combined with loss of scribble. The growth of these more aggressive tumor types is significantly, yet incompletely, suppressed by JNKmediated apoptosis. Remarkably, oncogenic Raf and JNK cooperate in these tumors, to induce massive hyperplasia in adjacent wildtype tissue. Thus, depending on the genetic context, JNK signaling can eradicate tumors by removing premalignant cells, or promote aberrant overgrowth in tissues surrounding primary lesions. http://www.ncbi.nlm.nih.gov/pubmed/16150723 Fri, 31 Dec 2004 00:00:00 -0800 Based on overexpression studies and target gene analyses, the transcription factor DNA replicationrelated element factor (DREF) has been proposed to regulate growth and replication in Drosophila melanogaster. Here we present lossoffunction experiments to analyze the contribution of DREF to these processes. RNA interferencemediated extinction of DREF function in vivo demonstrates a requirement for the protein for normal progression through the cell cycle and consequently for growth of imaginal discs and the derived adult organs. We show that DREF regulates the expression of genes that are required for the transition of imaginal disc cells through S phase. In conditions of suppressed apoptosis, DREF activation can cause overgrowth of developing organs. These data establish DREF as a global regulator of transcriptional programs that mediate cell proliferation and organ growth during animal development. http://www.ncbi.nlm.nih.gov/pubmed/15964814 Fri, 31 Dec 2004 00:00:00 -0800 The transcription factor AP1 positively controls synaptic plasticity at the Drosophila neuromuscular junction. Although in motor neurons, JNK has been shown to activate AP1, a positive regulator of growth and strength at the larval NMJ, the consequences of JNK activation are poorly studied. In addition, the downstream transcriptional targets of JNK and AP1 signaling in the Drosophila nervous system have yet to be identified. Here, we further investigated the role of JNK signaling at this model synapse employing an activated form of JNKkinase and using Serial Analysis of Gene Expression and oligonucleotide microarrays, searched for candidate early targets of JNK or AP1 dependent transcription in neurons. http://www.ncbi.nlm.nih.gov/pubmed/15932641 Fri, 31 Dec 2004 00:00:00 -0800 Aging of a eukaryotic organism is affected by its nutrition state and by its ability to prevent or repair oxidative damage. Consequently, signal transduction systems that control metabolism and oxidative stress responses influence life span. When nutrients are abundant, the insulin/IGF signaling (IIS) pathway promotes growth and energy storage but shortens life span. The transcription factor Foxo, which is inhibited by IIS, extends life span in conditions of low IIS activity. Life span can also be increased by activating the stressresponsive JunNterminal kinase (JNK) pathway. Here we show that JNK requires Foxo to extend life span in Drosophila. JNK antagonizes IIS, causing nuclear localization of Foxo and inducing its targets, including growth control and stress defense genes. JNK and Foxo also restrict IIS activity systemically by repressing IIS ligand expression in neuroendocrine cells. The convergence of JNK signaling and IIS on Foxo provides a model to explain the effects of stress and nutrition on longevity. http://www.ncbi.nlm.nih.gov/pubmed/15820683 Fri, 31 Dec 2004 00:00:00 -0800 Changes in the genetic makeup of an organism can extend lifespan significantly if they promote tolerance to environmental insults and thus prevent the general deterioration of cellular function that is associated with aging. Here, we introduce the Jun Nterminal kinase (JNK) signaling pathway as a genetic determinant of aging in Drosophila melanogaster. Based on expression profiling experiments, we demonstrate that JNK functions at the center of a signal transduction network that coordinates the induction of protective genes in response to oxidative challenge. JNK signaling activity thus alleviates the toxic effects of reactive oxygen species (ROS). In addition, we show that flies with mutations that augment JNK signaling accumulate less oxidative damage and live dramatically longer than wildtype flies. Our work thus identifies the evolutionarily conserved JNK signaling pathway as a major genetic factor in the control of longevity. http://www.ncbi.nlm.nih.gov/pubmed/14602080 Tue, 31 Dec 2002 00:00:00 -0800 http://www.ncbi.nlm.nih.gov/pubmed/12453405 Mon, 31 Dec 2001 00:00:00 -0800 Organogenesis involves cell proliferation followed by complex determination and differentiation events that are intricately controlled in time and space. The instructions for these different steps are, to a large degree, implicit in the gene expression profiles of the cells that partake in organogenesis. Combining fluorescenceactivated cell sorting and SAGE, we analyzed genomic expression patterns in the developing eye of Drosophila melanogaster. Genomic activity changes as cells pass from an uncommitted proliferating progenitor state through determination and differentiation steps toward a specialized cell fate. Analysis of the upstream sequences of genes specifically expressed during the proliferation phase of eye development implicates the transcription factor DREF and its inhibitor dMLF in the control of cell growth in this organ. http://www.ncbi.nlm.nih.gov/pubmed/12408803 Mon, 31 Dec 2001 00:00:00 -0800